Composite Rendering Question

I am new to composite rendering so I am not sure if I am even approaching this right. But what I have is a composition I want to render of a flying airplane (still image). I want to be able to render the propeller blur (using vector blur) separate from rendering the rest of the airplane, then composite the 2 together. Reason is that is a do a normal render using all layers for the airplane, it takes forever because it wants to do Motion/Vector Blur passes on the whole scene. So I want to render the prop separately. Any ideas to help a newbie?

I did something similar in Monster Movie so the Vector Blur node wouldn’t try to render the halo particles I used for dust effects – that would’ve taken centuries, I think :wink:

IIRC, if you put the prop on its own Render Layer separate from all other objects, you can then pipe just that Render Layer to the Vector Blur node, then use another node to re-combine the layers, such as Alpha Over, but you may have to create a new alpha channel for the blurred prop – not sure if the Vector Blur node will generate the alpha. You can do that with a node also. One of the Color combination nodes (like Mix or Add) may be useful, also.Something you’ll have to experiment with a bit.